We have measured dopamine-beta-hydroxylase (DBH), the enzyme which synthesizes norepinephrine from dopamine, in human cerebrospinal fluid (CSF) from psychiatric patients and normal volunteers. No significant differences were found among the mean CSF DBH values for several groups- primary affective disorder, schizophrenia, alcoholism, personality disorders, and normal volunteers. DBH and norepinephrine were highly correlated in CSF from depressed patients. Treatment of these patients with monoamine oxidase inhibitors, drugs which depress central noradrenergic firing, caused a significant decrease in CSF DBH. The activity of DBH in CSF may be an indicator of central noradrenergic activity.